This invention relates to the control of disc drives, and more particularly to the control of disc drives for data recording media such as floppy discs.
The personal computer or microcomputer is widely used for a variety of applications in the home, business, school and industry. Programs and external data storage for these computers are generally encoded on a flexible disc, called a floppy disc. The data on these discs is stored on a plurality of concentric tracks, which are arbitrary divisions of the surface of the disc which the computer can recognize by various embedded codes after the disc is formatted.
A disc drive for a floppy disc, or a hard disc, includes a motor for rotating the disc, a read/write head (or heads) for transferring data to and from the disc, a stepper motor for moving the read/write heads along the surface of the disc, and circuitry for interfacing between the computer and the motors and heads of the disc drive.
The floppy disc, if it has recording medium on both sides, can have tracks on both sides. In that case, read/write heads for both sides are required.
Whether or not both sides of the floppy disc has tracks, the tracks are each numbered for identification purposes. Certain extended capacity discs are available for the Apple II (Reg. TM) computer in the standard five and one-quarter inch size. The track numbers for these discs alternate sides, so that track "1" is on one side of the disc, track "2" is on the opposite side of the disc, and so on.
By way of example, disc drives used with the Apple II (Reg. TM) series of microcomputers are available in three information storage capacities: (1) standard density, 51/4" mini-floppy disc, (2) high density, 31/2" micro-floppy disc, and (3) hard disc density. The formats and densities of these discs are all different and, therefore, incompatible because of mechanical differences. One or two specific interface boards may be required to make them useable by the computer, according to the type of drive.
Some of this incompatibility could be eliminated if a greater disc storage capacity could be offered on the 51/4" mini-floppy disc while retaining 100% compatibility with the existing drives. Of course, such incompatibility should not be eliminated at the added cost of additional computer hardware, special interface cards, or special software.
Earlier attempts to provide users with greater storage capacity were only partially successful because the drives required special interface cards, or unreliable software modifications, or special software. To add further complication, these earlier high-capacity drives would not read a standard disc, and discs created in these earlier high-capacity drives could not be read in standard drives.